If there are a substantial amount of new people left to buy this thing (and there may well be), you'll chase away a good deal of them by releasing the game incomplete. People are distrustful of games getting split up like this (and for good reason) so it's going to hurt sales. And again if those sales are needed to fund the rest of the game, then it's more broken promises. It really just doesn't feel like the right decision for this particular game. In other cases where these companies are better funded, more trusted by consumers, etc it may be less problematic, but even then it's hard to guage the impact it has on sales.

Call it ridiculous, but it's happened countless times in the past. I bought Sin Episodes, Insecticide, Bone, Penny Arcade (which sort of finished in a radically different form, but still...).
Broken Age split their release up at great expense to the company, and luckily they can afford to do that, but it shouldn't be regarded as a guarantee. When companies split a game up to bankroll the remainder they often end up disappointed. Not only that, but I'd argue it undermines a game's ability to sell well; Broken Age should really have done much better considering its high profile and positive reviews, but it didn't because people don't want to buy half a game. They'll never make up the sales later, either since by the time it's whole, people will no longer care in the same way.
If you can guarantee (i.e. have the money and scheduling accounted for) that the whole game can be made, then there's no reason to split it up in the first place. Just make the whole thing. The problem is that companies split these releases up because they need money to finish the game, which is NOT a guarantee, and then they fuck themselves over in the process.

On the episodic games debate, I'd like to say this:
I enjoy the episodic game format, when it's done well, but the reality is that it's more demanding than normal game development, not less, and that's why so many have tried and failed. Episodic games have to be done on a pretty tight schedule, reliably, and consistently, often with two or more staggered teams all working together to make that possible. From a production standpoint, it's a major challenge.
When companies decide to release an episodic game because they simply don't have the time or resources to finish the game they're working on, it's usually a disaster. No one wants to buy the first episode of a game unless they're confident they know when the second episode is coming out. Even Broken Age, I'd guess, suffered much lower sales than many expected, probably for this very reason. People might be willing to "subscribe" to bi-monthly episodes, but they don't just want to buy half a game. If SpaceVenture went episodic, we'd never see the second episode. That's just the reality of the situation. They'd be better off releasing a "complete" game that's very short than a part 1 for which there will be no part 2. Full Throttle infamously ran over budget and had to cut out a huge chunk of the game, but imagine if they chose to go episodic instead. They'd be remembered for broken promises instead of a timeless classic that happens to be pretty short.

I don't think Paul is bipolar. I think he's exactly the same guy all the time. Which is to say, he doesn't really seperate how he is personally from professionally, or publicly from privately.
His comments about SpaceVenture would have been the sort of thing that would be fine to say in private, or even to say anonymously. SpaceVenture's biggest problem, development-wise, has been the fact that the project lacks a producer; there's no design document, no clear milestones or scheduling. Paul is a producer with a lot of experience and I can totally get why he'd have particularly strong opiniopns about that.
But whatever it is in most of us that would make it common sense not to post that under your own name in a public forum and not expect a backlash just isn't there in Paul. He doesn't have that filter.